1. Field of the invention
The present invention is directed to an optical instrument especially for gauging the velocity of a travelling surface of a body or a fluid. The gauging light beam emitted from a laser hits the surface, is reflected and stray reflections are received by a detector, processed by a computer and given as a read out of a velocity. Such an optical instrument or any other optical instrument comprises an optical assembly which is carried by a stage plate. The invention concerns in particular the support of the stage plate carrying an optical assembly.
2. Description of the prior art
One of the fields where optical instruments as initially described are used is the rolling of rails from steel blocks. Since the beginning and the end of a rail in the process of being rolled is detected by the optical instrument and since the velocity of travelling is gauged the length of the rail can be computered within an instant. The optical instrument cannot be placed too far away from the rolling action, and therefore measurements have to be taken to maintain the accuracy of the optical instrument by excluding too much thermal stresses.
One known optical instrument for the contactless gauging of the velocity and the length of an object with the aid of a laser beam has a robust cast aluminium housing which has to be cooled by water. The housing consists of a thick-walled base and lateral as well as frontal plates in which the cooling water of the cooling system can circulate. Despite these efforts heat creeps into the structure, because not all areas of the housing can be reached by the cooling system so that distortions may occur. These distortions compromise the optical assembly for the focussing and guiding of the laser beam.
There are gauging systems with two beams or one beam and in the latter case there is a reference beam. In any case, the gauging light beam which is split, reflected and focussed and the stray reflections have to be passed through several optical components like lenses, mirrors and other optical aids which have to be positioned extremely accurate one to the other. If an accurate positioning is distorted by a mechanical attack or by heat deformation the quality of the instrument suffers severely. The velocity is measured by gauging the frequency of a surge received from overlapping the original frequency and the frequency of the stray reflections modified by the Doppler-effect.